1. Technical Field
The present invention relates to platen preparation systems and, more particularly, to a system for texturizing and charging a platen that includes the ability to accurately control various system parameters.
2. Description of the Related Art
Lapping machines are commonly used to perform lapping operations on various work materials such as semiconductor wafers, magnetic disk substrates, magnetic head units, etc. Such lapping machines utilize a lapping plate that performs grinding and/or polishing operations on the work material. Current trends for miniaturization and increased capacity of hard disk drives has resulted in the need for materials having a high degree of planarity, while maintaining close tolerances. Consequently, lapping plates used to grind and polish such materials must be constructed with a high degree of precision.
Lapping plates are typically constructed such that one, or both, surfaces contain predetermined concentrations of abrasive materials. The lapping plate is sometimes used in conjunction with a slurry containing abrasive material during the grinding, or lapping, operations. Over time, the abrasive contained in the lapping plate becomes worn, and reduces the effectiveness of the lapping plate. Accordingly, the material and design of the lapping plate are important for improving its useful life, and reducing manufacturing costs.
Various types of materials and methods have been employed for constructing the abrasive surface of lapping plates. For example, the abrasive surface is often formed by embedding diamond particles into the lapping plate in a process known as charging. Diamond particles tend to provide superior resistance to wear due to their hardness properties. The procedure for embedding diamond particles into lapping plates ranges from hand charging with a tool to charging on a lapping machine with various tools. Additionally, metal bonded diamond plated conditioning rings have been used to texturize lapping plates. The conditioning ring typically consists of a metallic ring having one face coated with a monolayer of diamond that is held in place by an electroplated nickel deposit.
There currently exists no systems specifically designed for preparing lapping plates. Current devices are in the form of lapping machines that have been modified for use to prepare a platen for lapping operations. Such devices have drawbacks when used to prepare lapping plates. For example, the process of preparing a lapping plate requires several processing steps, and modifications must be made to the device for each process step. The resulting lapping plate is somewhat deficient because the device cannot be optimized for each process step.
There are various examples in the literature that describe processes for charging lapping plates. For example, U.S. Pat. No. 5,107,626 issued to Mucci describes a method of providing a patterned surface on a substrate using an abrasive article having a specified pattern. The abrasive article includes a backing having at least one abrasive composite bonded thereto. The abrasive composite is in the form of abrasive grains dispersed in a binder and are disposed in a predetermined array consisting of a plurality of peaks and valleys.
U.S. Pat. Nos. 4,866,886 and 4,821,461 issued to Holmstrand both describe a lapping plate that is selectively textured for improved useful life and greater abrading consistency. Glass beads are serially propelled onto a lapping surface of the lapping plate to form spherical cavities of uniform size and distribution, as well as a desired density. The cavities provide discontinuity in the lapping surface which substantially prevents hydroplaning. The cavities also receive loose abrading grit, workpiece fragments, and other contaminants that result in more smoothly machined workpiece surfaces.
There are various other examples of devices for preparing lapping plates. For example, see U.S. Pat. Nos. 3,680,265; 3,903,653; 4,418,501; 5,713,123; and 5,749,769. None of the conventional devices, however, are designed for preparing lapping plates. Consequently, these devices are incapable of optimizing performance of the lapping plate. Additionally, these devices do not minimize the impact of contacting a tool to the surface of a platen.
Accordingly, there exists a need for a platen preparation system that is specifically designed to prepare and, hence, optimize performance of lapping plates. There is also a need to reduce the impact force of a tool upon the surface of a platen in order to minimize damage to the platen surface.
An advantage of the present invention is a platen preparation system that is specifically designed to prepare a platen for performing lapping operations.
This and other advantages are achieved by the present invention wherein a system for preparing a platen for lapping operations includes a mechanism for slowing the descent of a tool towards the surface of a platen in order to lighten the impact of the tool upon the surface of the platen.
According to one aspect of the invention, an apparatus for preparing platens for lapping operations comprises: a base, a platter, a main drive motor, at least one pressure arm, a tool attached to each pressure arm, an actuator coupled to each pressure arm, a mechanism for slowing each pressure arm to reduce impact of the tool on the platen, and a monitor. The platter is rotatably mounted on the base and designed to receive the platen thereon. The main drive motor is attached to the base and operatively coupled to the platter so that the platter, and platen disposed thereon, can be rotated. The pressure arms are disposed on the base and include a tool receiving portion that can be positioned in alignment with the lapping surface of the platen. A tool is attached to each tool receiving portion so that predetermined operations can be performed on the lapping surface of the platen. The actuators place the pressure arms in contact with the lapping surface of the platen, and slow the descent of the tool onto the platen to reduce impact, then apply prescribed pressure levels to perform various operations. During selected operations, the monitor monitors predetermined criteria to maintain substantially constant conditions. According to such a system, a high quality lapping plate can be prepared using a single device. Further, by monitoring certain criteria to maintain constant conditions, lapping plates can be prepared with repeated consistency and quality.
According to another aspect of the invention, a method for reducing impact of a tool upon a platen surface comprises the steps of: lowering the tool; detecting the presence of the tool at a height above the platen surface; and stopping the lowering of the tool based upon detecting the tool at the height above the platen surface.
According to another aspect of the invention, a method for reducing impact of a tool upon a platen surface comprises the steps of: lowering the tool; and initiating stopping lowering the tool based upon initial contact of the tool with the platen surface.
Additional advantages and novel features of the present invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the present invention. The embodiments shown and described provide an illustration of the best mode contemplated for carrying out the present invention. The invention is capable of modifications in various obvious respects, all without departing from the spirit and scope thereof. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive. The advantages of the present invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.